Instruction Manual

A-121

VCF 2

System A - 100

doepfer

Resonance

Another filter parameter is resonance, also known as

emphasis or Q. As the value for Q gets higher, the

frequencies around the cut-off frequency f

are em-

phasised. Fig. 2 shows this process using a low-pass

filter as an example (a high-pass filter would produce a

mirror-image). This way, you can make the frequen-

cies around the cut-off point stand out more.

Fig. 2: How resonance affects the response of a

filter around the cut-off frequency.

In band-pass mode, an increase in Q’s value makes

the bandwidth narrower.

The same is true of notch mode, but of course in this

case this narrower band will be rejected, instead of let

through.

Setting the resonance close to maximum sends the

filter into self oscillation, and makes it behave like a

sine wave oscillator.

The A-121’s resonance is not frequency de-

pendent to any significant degree. As long as

resonance is kept below the self-oscillation

level, any variation is imperceptible.

The one exception to this is at high levels of

resonance, coupled with a high cut-off fre-

quency setting, when an increase in reso-

nance can lead to a small drop in the sine-

wave output’s frequency. This is a characte-

ristic of the CEM 3320 filter IC, and is not

due to a design fault in the A-121’s control

system.

Resonance

Frequency

➨

➨➨

➨

0 db